Database System Notes
Database and File System are two methods used to store, retrieve, manage and manipulate
data. Both systems can be used to allow the user to work with data in a similar way. A File
System is a collection of raw data files stored in the hard-drive, whereas a database is
intended for easily organizing, storing and retrieving large amounts of data. In other words,
a database holds a bundle of organized data (typically in a digital form) for one or more
users. Databases, often abbreviated DB, are classified according to their content, such as
document-text, bibliographic and statistical. It should be noted that, even in a database, data
are eventually (physically) stored in some sort of files.
What is a File system?
As mentioned above, in a typical File System electronic data are directly stored in a set of
files. If only one table is stored in a file, it is called a flat file. They contain values in each row
separated with a special delimiter like commas. In order to query some random data, first it
is required to parse each row and load it to an array at run time, but for this file should be
read sequentially (because, there is no control mechanism in files); therefore it is quite
inefficient and time consuming. The burden of locating the necessary file, going through the
records (line by line), checking for the existence of a certain data and remembering what
files/records to edit are on the user. The user either has to perform each task manually or
has to write a script that does them automatically with the help of the file management
capabilities of the operating system. Because of these reasons, File Systems are easily
vulnerable to serious issues like inconsistency, inability to maintain concurrency, data
isolation, threats on integrity and lack of security.
What is a Database?
A database is a collection of information stored, that is organized so that it can easily be
accessed, managed, and updated.
A Database may contain different levels of abstraction in its architecture. Typically, the
three levels: external, conceptual and internal make up the database architecture. External
level defines how the users view the data. A single database can have multiple views. The
internal level defines how the data is physically stored. The conceptual level is
the communication medium between internal and external levels. It provides a unique view
of the database regardless of how it is stored or viewed. There are several types of
databases such as Analytical databases, Data warehouses and Distributed databases.
Databases (more correctly, relational databases) are made up of tables, and they contain
rows and columns, much like spreadsheets in Excel. Each column corresponds to an
attribute while each row represents a single record. For example, in a database, which
stores employee information of a company, the columns could contain employee name,
employee Id and salary, while a single row represents a single employee. Most databases
come with a Database Management System (DBMS) that makes it very easy to
create/manage/organize data.
What is the difference between File system and Database?
As a summery, in a File System, files are used to store data while, a database is a collection
of organized data. Although File System and databases are two ways of managing data,
databases clearly have many advantages over File Systems. Typically when using a File
System, most tasks such as storage, retrieval and search are done manually (even though
,most operating systems provide graphical interfaces to make these tasks easier) and it is
quite tedious whereas when using a database, the inbuilt DBMS will provide automated
methods to complete these tasks.
Because of this reason, using a File System will lead to problems like data integrity, data
inconsistency and data security, but these problems could be avoided by using a database.
Unlike a File System, databases are efficient because reading line by line is not required, and
certain control mechanisms are in place.
Disadvantages of File Systems
Data redundancy is found- the presence of duplicate data in multiple data files e.g.
Customer Name, NI number, Address is present in several different files on several
different systems. Errors are generated, time entering data is wasted, computer
resources are needlessly taken up and updates can be an enormous problem.
Data inconsistency will become a problem e.g. information is duplicated in each
system and may be updated in most systems but not necessarily in all – the savings
account and loan account may have different addresses for a particular customer.
Lack of data independence. (Data dependence refers to the close relationship
between data stored in files and the specific software programs needed to update
and maintain those files). In the bank imagine cases where any change in data
format or structure requires a change in all the programs that access the data. E.g.
effort required to change from 3-digit STD to 4-digit STD may be very difficult.
Data lacks integrity, i.e. this is the quality by which information from the system
can be trusted. The problems already stated show that information can be out of
date, can have different values in different parts of the system, can be inaccurate etc.
Lack of flexibility i.e. creating reports, e.g. in this system a summary of account
balances in each separate account would require separate reports for each open
account or cutting and pasting into a word processor file – not a satisfactory state of
affairs.
Data not shareable. Similarly if different departments want to access data this
would be very awkward.
Main Functions of Databases System.
Facilitate remote data entry.
Facilitate information and resource sharing.
Facilitate long term and large amount of information storage
Facilitate centralized information storage.
A DBMS (Database management System) Vs Database Systems (DBS)
A DBMS is application software that lets you create, organize, update, store, and
retrieve data from a single database or several databases. Lets you transform or map
data from one model to another, or between the central model and stored database
while database is a collection of information stored, that is organized so that it can
easily be accessed, managed, and updated.
There are many functions a Database Management System (DBMS) serves that are key
components to the operation of database management. When deciding to implement a
DBMS in your business, first you must decide what type of DBMS you want. Common types
,of DBMS are the relational, network, hierarchy and object oriented models. Each kind of
database structure has its own pros and cons.
While each is unique in its own way, there are some standard functions of a DBMS, and
these are:
The ability to update and retrieve data
This is a fundamental component of a DBMS and essential to database management.
Without the ability to view or manipulate data, there would be no point to using a database
system.
Updating data in a database includes adding new records, deleting existing records and
changing information within a record. The user does not need to be aware of how DBMS
structures this data, all the user needs to be aware of is the availability of updating and/or
pulling up information, the DBMS handles the processes and the structure of the data on a
disk.
Support Concurrent Updates
Concurrent updates occur when multiple users make updates to the database
simultaneously. Supporting concurrent updates is also crucial to database management as
this component ensures that updates are made correctly and the end result is accurate.
Without DBMS intervention, important data could be lost and/or inaccurate data stored.
DBMS uses features to support concurrent updates such as batch processing, locking, two-
phase locking, and time stamping to help make certain that updates are done accurately.
Again, the user is not aware all this is happening as it is the database management system’s
responsibility to make sure all updates are stored properly.
Backup and recovery of Data
In the event a catastrophe occurs, DBMS must provide ways to recover a database so that
data is not permanently lost. There are times computers may crash, a fire or other natural
disaster may occur, or a user may enter incorrect information invalidating or making
records inconsistent.
If the database is destroyed or damaged in any way, the DBMS must be able to recover the
correct state of the database, and this process is called Recovery. The easiest way to do this
is to make regular backups of information. This can be done at a set structured time so in
the event a disaster occurs, the database can be restored to the state that it was last at prior
to backup.
A disadvantage to this is any data or changes entered after the backup would be lost. A way
to counteract this is to set the DBMS to provide a feature called Journaling. This involves
keeping a log of all updates made to the database, it is maintained in a file separate from the
, database and can be obtained to re-update the database after it is recovered from the
backup.
Security
Security is the prevention of unauthorized users accessing the database. DBMS uses
features such as encryption, authentication, authorization and views to provide security to
the database. Encryption is when DBMS converts the data in a database to an
indecipherable format. No unauthorized person trying to access this information will be
able to read it. Authorized users will be able to see it in normal form.
Authentication is a technique in which the database administrator can identify the person
accessing the database. Authorized users are given passwords and successful entry of a
valid password will allow the user entry into the database, if a password is not successfully
entered, the user will be denied access. Authorization is a set of rules that the database
administrator (DBA) sets up to specify levels of usage that individuals or groups are allowed
to have. Some users may only be allowed viewing options, while others may be allowed to
both view/make changes.
In some circumstances, users may only be allowed to access certain pieces of the database,
and be denied access to areas that does not relate to their specific needs. In these cases, the
DBA will assign workgroups, and these workgroups will be assigned levels of access and
permissions. Views are when DBA allows certain users the ability to view the tables or fields
that pertain to them, any other view does not exist for them in the database, DBMS does this
behind the scenes and to the user it appears that the information they see are the only
existing data.
Data Integrity
Data integrity is an important function in database management. This is a set of rules that
DBMS provides to see that data integrity is enforced, thus avoiding incorrect or inconsistent
data. Types of integrity that DBMS provides are data type, legal values and format. Key
integrity also falls into this function of DBMS. This enforces that the primary key of a record
remains unique.
Without any of the above listed functions, a database would not be able to work effectively.
Each of these functions plays an important role in database management. And many more
such as
Builds the database – creates and maintains the database schema.
Manages the database - has to ensure problems do not arise if two people simultaneously
access a record and try to update it.
Governs interactions between application programs, input data and the database itself i.e.
allows users to store, retrieve and update as easily as possible without having to be aware
of the internal structure of the database.
Database and File System are two methods used to store, retrieve, manage and manipulate
data. Both systems can be used to allow the user to work with data in a similar way. A File
System is a collection of raw data files stored in the hard-drive, whereas a database is
intended for easily organizing, storing and retrieving large amounts of data. In other words,
a database holds a bundle of organized data (typically in a digital form) for one or more
users. Databases, often abbreviated DB, are classified according to their content, such as
document-text, bibliographic and statistical. It should be noted that, even in a database, data
are eventually (physically) stored in some sort of files.
What is a File system?
As mentioned above, in a typical File System electronic data are directly stored in a set of
files. If only one table is stored in a file, it is called a flat file. They contain values in each row
separated with a special delimiter like commas. In order to query some random data, first it
is required to parse each row and load it to an array at run time, but for this file should be
read sequentially (because, there is no control mechanism in files); therefore it is quite
inefficient and time consuming. The burden of locating the necessary file, going through the
records (line by line), checking for the existence of a certain data and remembering what
files/records to edit are on the user. The user either has to perform each task manually or
has to write a script that does them automatically with the help of the file management
capabilities of the operating system. Because of these reasons, File Systems are easily
vulnerable to serious issues like inconsistency, inability to maintain concurrency, data
isolation, threats on integrity and lack of security.
What is a Database?
A database is a collection of information stored, that is organized so that it can easily be
accessed, managed, and updated.
A Database may contain different levels of abstraction in its architecture. Typically, the
three levels: external, conceptual and internal make up the database architecture. External
level defines how the users view the data. A single database can have multiple views. The
internal level defines how the data is physically stored. The conceptual level is
the communication medium between internal and external levels. It provides a unique view
of the database regardless of how it is stored or viewed. There are several types of
databases such as Analytical databases, Data warehouses and Distributed databases.
Databases (more correctly, relational databases) are made up of tables, and they contain
rows and columns, much like spreadsheets in Excel. Each column corresponds to an
attribute while each row represents a single record. For example, in a database, which
stores employee information of a company, the columns could contain employee name,
employee Id and salary, while a single row represents a single employee. Most databases
come with a Database Management System (DBMS) that makes it very easy to
create/manage/organize data.
What is the difference between File system and Database?
As a summery, in a File System, files are used to store data while, a database is a collection
of organized data. Although File System and databases are two ways of managing data,
databases clearly have many advantages over File Systems. Typically when using a File
System, most tasks such as storage, retrieval and search are done manually (even though
,most operating systems provide graphical interfaces to make these tasks easier) and it is
quite tedious whereas when using a database, the inbuilt DBMS will provide automated
methods to complete these tasks.
Because of this reason, using a File System will lead to problems like data integrity, data
inconsistency and data security, but these problems could be avoided by using a database.
Unlike a File System, databases are efficient because reading line by line is not required, and
certain control mechanisms are in place.
Disadvantages of File Systems
Data redundancy is found- the presence of duplicate data in multiple data files e.g.
Customer Name, NI number, Address is present in several different files on several
different systems. Errors are generated, time entering data is wasted, computer
resources are needlessly taken up and updates can be an enormous problem.
Data inconsistency will become a problem e.g. information is duplicated in each
system and may be updated in most systems but not necessarily in all – the savings
account and loan account may have different addresses for a particular customer.
Lack of data independence. (Data dependence refers to the close relationship
between data stored in files and the specific software programs needed to update
and maintain those files). In the bank imagine cases where any change in data
format or structure requires a change in all the programs that access the data. E.g.
effort required to change from 3-digit STD to 4-digit STD may be very difficult.
Data lacks integrity, i.e. this is the quality by which information from the system
can be trusted. The problems already stated show that information can be out of
date, can have different values in different parts of the system, can be inaccurate etc.
Lack of flexibility i.e. creating reports, e.g. in this system a summary of account
balances in each separate account would require separate reports for each open
account or cutting and pasting into a word processor file – not a satisfactory state of
affairs.
Data not shareable. Similarly if different departments want to access data this
would be very awkward.
Main Functions of Databases System.
Facilitate remote data entry.
Facilitate information and resource sharing.
Facilitate long term and large amount of information storage
Facilitate centralized information storage.
A DBMS (Database management System) Vs Database Systems (DBS)
A DBMS is application software that lets you create, organize, update, store, and
retrieve data from a single database or several databases. Lets you transform or map
data from one model to another, or between the central model and stored database
while database is a collection of information stored, that is organized so that it can
easily be accessed, managed, and updated.
There are many functions a Database Management System (DBMS) serves that are key
components to the operation of database management. When deciding to implement a
DBMS in your business, first you must decide what type of DBMS you want. Common types
,of DBMS are the relational, network, hierarchy and object oriented models. Each kind of
database structure has its own pros and cons.
While each is unique in its own way, there are some standard functions of a DBMS, and
these are:
The ability to update and retrieve data
This is a fundamental component of a DBMS and essential to database management.
Without the ability to view or manipulate data, there would be no point to using a database
system.
Updating data in a database includes adding new records, deleting existing records and
changing information within a record. The user does not need to be aware of how DBMS
structures this data, all the user needs to be aware of is the availability of updating and/or
pulling up information, the DBMS handles the processes and the structure of the data on a
disk.
Support Concurrent Updates
Concurrent updates occur when multiple users make updates to the database
simultaneously. Supporting concurrent updates is also crucial to database management as
this component ensures that updates are made correctly and the end result is accurate.
Without DBMS intervention, important data could be lost and/or inaccurate data stored.
DBMS uses features to support concurrent updates such as batch processing, locking, two-
phase locking, and time stamping to help make certain that updates are done accurately.
Again, the user is not aware all this is happening as it is the database management system’s
responsibility to make sure all updates are stored properly.
Backup and recovery of Data
In the event a catastrophe occurs, DBMS must provide ways to recover a database so that
data is not permanently lost. There are times computers may crash, a fire or other natural
disaster may occur, or a user may enter incorrect information invalidating or making
records inconsistent.
If the database is destroyed or damaged in any way, the DBMS must be able to recover the
correct state of the database, and this process is called Recovery. The easiest way to do this
is to make regular backups of information. This can be done at a set structured time so in
the event a disaster occurs, the database can be restored to the state that it was last at prior
to backup.
A disadvantage to this is any data or changes entered after the backup would be lost. A way
to counteract this is to set the DBMS to provide a feature called Journaling. This involves
keeping a log of all updates made to the database, it is maintained in a file separate from the
, database and can be obtained to re-update the database after it is recovered from the
backup.
Security
Security is the prevention of unauthorized users accessing the database. DBMS uses
features such as encryption, authentication, authorization and views to provide security to
the database. Encryption is when DBMS converts the data in a database to an
indecipherable format. No unauthorized person trying to access this information will be
able to read it. Authorized users will be able to see it in normal form.
Authentication is a technique in which the database administrator can identify the person
accessing the database. Authorized users are given passwords and successful entry of a
valid password will allow the user entry into the database, if a password is not successfully
entered, the user will be denied access. Authorization is a set of rules that the database
administrator (DBA) sets up to specify levels of usage that individuals or groups are allowed
to have. Some users may only be allowed viewing options, while others may be allowed to
both view/make changes.
In some circumstances, users may only be allowed to access certain pieces of the database,
and be denied access to areas that does not relate to their specific needs. In these cases, the
DBA will assign workgroups, and these workgroups will be assigned levels of access and
permissions. Views are when DBA allows certain users the ability to view the tables or fields
that pertain to them, any other view does not exist for them in the database, DBMS does this
behind the scenes and to the user it appears that the information they see are the only
existing data.
Data Integrity
Data integrity is an important function in database management. This is a set of rules that
DBMS provides to see that data integrity is enforced, thus avoiding incorrect or inconsistent
data. Types of integrity that DBMS provides are data type, legal values and format. Key
integrity also falls into this function of DBMS. This enforces that the primary key of a record
remains unique.
Without any of the above listed functions, a database would not be able to work effectively.
Each of these functions plays an important role in database management. And many more
such as
Builds the database – creates and maintains the database schema.
Manages the database - has to ensure problems do not arise if two people simultaneously
access a record and try to update it.
Governs interactions between application programs, input data and the database itself i.e.
allows users to store, retrieve and update as easily as possible without having to be aware
of the internal structure of the database.
